The present invention relates to an apparatus and method for taking a sample of downhole fluid.
In oil and gas operations it is often necessary to take samples of fluid from the downhole well bore. These samples can then be brought back to the surface for analysis. Such procedures are commonly used during well-bore clean up operations to verify cleanliness and the effectiveness of said operations.
Various tools have been developed for the purpose of taking downhole fluid samples. Typically these tools comprise a sampling means which is run into a well bore on a tubing string in combination with a packer means for isolating a well annulus portion. The tool comprises an activation means which is usually biased into a closed position and can be moved from the closed position to an open position by a pressure change or electrical signal.
In the open position the sampling means communicates with the isolated well bore annulus to allow a sample of the downhole contents to be taken. The activation means returns to the closed position via the bias means when the previously applied pressure or electrical signal is removed or terminated. In other tools where the activation means is not biased into a closed position, the electrical signal or pressure increase is applied further to move the activation means to a second closed position, after the sample has been taken.
A disadvantage of conventional sampler tools lies in the fact that efficient working of these tools relies on the bias means functioning properly to re-close the moveable activation means, or a further increase in pressure (pressuring-up) or electrical signal to close the sampling means. Where the sample is required from a particular area or depth within the well it is essential that the sampling means is closed as the tool is removed or tripped from the hole so that the sample is not lost or contaminated.
It is an object of the present invention to provide an improved sampling tool for collecting samples of fluid in a downhole environment and bringing said samples to the surface.
According to a first aspect of the present invention there is provided a downhole sampler tool for extracting a sample of fluid from a well bore, the sampler tool being comprised of a cylindrical body connectable on a workstring, the body having a throughbore therein, an outer sleeve arranged on the body and an activation means, wherein the activation means causes the outer sleeve to be moved axially from a first to a second position thereby creating a sampling chamber into which the sample of fluid is drawn.
Preferably the tool further includes a non return valve through which the fluid is drawn into the chamber as the outer sleeve is moved.
Preferably the tool also comprises a locking means which locks the outer sleeve into the second position.
Advantageously the locking means comprises a snap ring into which a portion of the outer sleeve engages in the second position.
Typically the activation means comprises a drop ball which communicates with a drop ball seat in the tool.
Preferably the tool further includes an inner sleeve located in the throughbore the inner sleeve being interconnected to the outer sleeve. The inner and outer sleeves may be mechanically coupled by way of a bolt, for example. Thus the activation means may cause the movement of the outer sleeve by virtue of moving the inner sleeve.
Advantageously the tool also comprises a by pass means to allow circulation of fluid through the throughbore of the cylindrical body after the fluid sample has been taken. Preferably the by pass means is a fluid passage accessed by movement of a by pass sleeve by the activation means.
In order to prevent movement of any of the sleeves when the tool is deployed the sleeves may be held in the first position by shear pins which shear on action of the drop ball.
According to a second aspect of the present invention there is provided a method of taking a fluid sample downhole comprising the steps of:
a) running a fluid sampler tool downhole;
b) activating the tool to create a chamber into which the fluid sample is drawn; and
c) retrieving the tool with the fluid sample.
Preferably the method includes the step of drawing the fluid through a one-way valve to seal the fluid sample in the chamber.
Preferably also the method includes the step of locking the tool after the sample has been taken so that the chamber is fixed before retrieval.
Typically the method includes the step of activating the tool is achieved by a drop ball mechanism.
According to a third aspect of the present invention there is provided a method of taking a fluid sample downhole comprising the steps of:
a) running a fluid sampler tool downhole; the fluid sampler tool having a cylindrical body, throughbore, drop ball seat and moveable inner and outer sleeves which are mechanically connected and held to the body by shear pins;
b) rupturing said shear pins to allow said inner and outer sleeves to move relative to the body by landing a drop ball in the drop ball seat, wherein movement of the inner and outer sleeves creates a chamber having a one way valve into which downhole fluid is drawn; and
c) retrieving the fluid sampler tool containing the fluid sample in the chamber means.